Abscesses of the liver
DEFINITION AND CLASSIFICATION
A liver abscess is a localised collection of pus within hepatic parenchyma. It is classified as pyogenic (usually bacterial), amoebic (Entamoeba histolytica) or, less commonly, fungal. Abscesses may be solitary or multiple and are more frequent in the right lobe because of its greater volume and portal flow.
AETIOLOGY AND PATHOGENESIS
Pyogenic infection reaches the liver by ascending biliary infection (e.g. obstruction, stones, strictures or malignancy), portal spread from intra-abdominal infection, hepatic arterial bacteraemia, direct extension, trauma or following intervention. Common organisms include enteric Gram-negative bacilli, streptococci, enterococci and anaerobes; Klebsiella pneumoniae is important in some settings. Amoebic abscess follows intestinal invasion by E. histolytica and portal dissemination; it classically contains sterile-looking brown 'anchovy paste' material. Diabetes, malignancy, immunosuppression and biliary disease increase risk.
CLINICAL FEATURES
Typical features are fever, rigors, right-upper-quadrant pain and tenderness, malaise, anorexia and weight loss. Hepatomegaly may be present. Jaundice is more likely with biliary obstruction or extensive disease. A high right-sided abscess can irritate the diaphragm, causing pleuritic pain, cough or right shoulder pain. Elderly or immunocompromised patients may present with sepsis and few localising signs.
INVESTIGATIONS
Blood tests commonly show neutrophilic leukocytosis, raised CRP/ESR, alkaline phosphatase elevation and variable transaminase or bilirubin changes. Obtain blood cultures before antibiotics if this does not delay treatment. Ultrasound detects collections and guides drainage; contrast CT is highly useful for defining size, number, gas, loculations and source. Aspirated pus should be sent for Gram stain and aerobic/anaerobic culture. Consider amoebic serology and stool testing according to epidemiology; stool microscopy may be negative in isolated hepatic disease.
DIFFERENTIAL DIAGNOSIS
Consider infected hydatid cyst, necrotic primary or metastatic tumour, hepatocellular carcinoma, biliary cyst, haematoma and subphrenic abscess. Imaging, clinical context, serology and aspirate findings help distinguish them. Do not assume every cystic liver lesion is an abscess.